Question

An amorphous solid “A” burns in air to form a gas “B” which turns lime water milky. The gas is also produced as a by-product during roasting

Answer 1

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Question :

An amorphous solid “A” burns in air to form a gas “B” which turns lime water milky. The gas is also produced as a by-product during roasting of sulphide ore. This gas decolourises acidified aqueous KMnO₄ solution and reduces Fe³⁺ to Fe²⁺. Identify the solid ''A'' and the gas ''B'' an write the reactions involved.

Answer :

         (1) Since gas ''B'' is obtained as a by-product during roasting of sulphide, therefore, gas ''B'' must be SO₂

             2 ZnS + 3 O₂ -----> 2 ZnO + 2 SO₂ (B)

        (2) Since gas ''B'' is obtained when amorphous solid ' A ' burns in air, therefore, amorphous solid 'A' must be sulphur, S₈

           S₈ (A) + 8 O₂ ------> 8 SO₂ (B)

      (3) Gas "B'' reduced acidified KMnO₄ solution and reduces Fe³⁺ to Fe⁺⁺ salts as shown below:

         2 MnO₄⁻ + 5 SO₂ + 2 H₂O --------> 2 Mn²⁺ + 5 SO₄²⁻ + 4 H⁺

        (Purple)         (B)                            (Colourless)

         2 Fe³⁺  + SO₂ + 2H₂O --------> 2 Fe²⁺ + SO₄²⁻  + 4 H⁺

        (Yellow)    (B)                          (Green)

GOOD LUCK !!

Answer 2

Answer:

(1) Since gas ''B'' is obtained as a by-product during roasting of sulphide, therefore, gas ''B'' must be SO₂

            2 ZnS + 3 O₂ -----> 2 ZnO + 2 SO₂ (B)

       (2) Since gas ''B'' is obtained when amorphous solid ' A ' burns in air, therefore, amorphous solid 'A' must be sulphur, S₈

          S₈ (A) + 8 O₂ ------> 8 SO₂ (B)

     (3) Gas "B'' reduced acidified KMnO₄ solution and reduces Fe³⁺ to Fe⁺⁺ salts as shown below:

        2 MnO₄⁻ + 5 SO₂ + 2 H₂O --------> 2 Mn²⁺ + 5 SO₄²⁻ + 4 H⁺

       (Purple)         (B)                            (Colourless)

        2 Fe³⁺  + SO₂ + 2H₂O --------> 2 Fe²⁺ + SO₄²⁻  + 4 H⁺

       (Yellow)    (B)                          (Green)